1. Field of the Invention
The present invention relates to an X-ray microscope apparatus and, more particularly, to an X-ray microscope apparatus capable of forming an enlarged X-ray image of a specimen held in contact condition.
2. Description of the Related Art
Some of X-ray microscopes that form a high-resolution transmission image of an object by using X-rays of short wavelengths having high penetrating power use an X-ray imaging device and the others do not. X-ray imaging devices include Fresnel zone plates, grazing incidence mirrors, etc. Since the X-ray imaging device has low converging power, the focal length of an X-ray magnification optical system is inevitably long and hence the X-ray microscope has a big overall length. Although the resolution of the most advanced zone plate system is 50 nm, the zone plate system needs a light source capable of emitting intense light, such as synchrotron radiation, because the condensing efficiency of the X-ray imaging device is low. Since it is difficult to provide an X-ray imaging device with a zooming function that enables magnification adjustment, another image enlarging device, such as an optical microscope, must be used in combination with the X-ray imaging device to specify the observation position of the object, which requires troublesome operations.
Some of the X-ray microscopes not using the X-ray imaging device use a projection enlargement method of observing a projected image formed by diverging X-rays emitted by a point light source and transmitted trough a specimen placed near the point light source, while the others use a contact imaging method of observing an enlarged X-ray image obtained by magnifying an image formed by irradiating a specimen held in contact with a photoresist plate with X-rays, and developing a latent image and enlarging by a proper optical system.
The projection enlargement method inevitably involves penumbral blurring due to the size of the X-ray source and diffraction blurring due to the specimen. Therefore, the practical resolution of the projection enlargement method is in the range of about 0.1 to 0.2 μm.
The contact imaging method does not use any X-ray enlarging optical system and hence does not cause any aberration and the image of the specimen is blurred scarcely because the specimen is held in contact with the photoresist plate. Thus, in principle, the contact imaging method is able to form easily an image of a high resolution. The resolution achievable by the contact imaging method is dependent on the particle size of the photoresist. The contact imaging method is able to form images of a high resolution of 10 nm or below when an X-ray resist of a high resolution. However, since the photoresist plate in the present state has a very low sensitivity, an X-ray source capable of emitting intense X-rays is necessary. The observation of an enlarged X-ray image needs troublesome operations for taking the photoresist plate out of a vacuum vessel, forming an X-ray image by a developing process, and enlarging the developed X-ray image by an optical microscope or the like for observation. Since the vacuum of the vacuum vessel needs to be broken in taking the photoresist plate out of the vacuum vessel, many X-ray images cannot continuously be obtained.
X-ray microscope apparatuses disclosed in JP-A Nos. 117252/1989 and 29600/1996 enlarge an X-ray image obtained by irradiating a specimen with X-rays by an X-ray imaging device to obtain an enlarged X-ray image, project the enlarged X-ray image on a photocathode to convert the X-ray image into an electron image, enlarge the electron image by the agency of magnetic lenses to obtain an enlarged electron image, project the enlarged electron image on a fluorescent screen to form an optical image on the fluorescent screen, and photograph the optical image by a camera to obtain a picture for observation. These previously disclosed X-ray microscope apparatuses using X-ray enlargement, electronic enlargement and optical enlargement do not need any developing process and any other microscope for the observation of enlarged images, and are capable of forming a large image obtained by magnifying an original image at a very high magnification in a real-time mode.
However, those known X-ray microscope apparatuses using the X-ray enlarging optical system are large and cannot be installed in a narrow place.